In-stream data sets

An in-stream data set is a data set contained within a set of JCL statements. In-stream data sets (also called inline data sets) begin with a DD * or DD DATA statement. These DD statements can have any valid ddname, including SYSIN. If you omit a DD statement before the input data, the system provides a DD * statement with the ddname of SYSIN. This example shows you how to indicate an in-stream data set: 
   //MYDD    DD *
   record 1
   record 2
   record 3
   /*
The // at the beginning of the data set starts in column 1. The statement fopen("DD:MYDD","rb"); opens a data set with lrecl=80, blksize=80, and recfm=FB. In this example, the delimiter indicating the end of the data set is /*. In some cases, your data may contain this string. For example, if you are using C source code that contains comments, z/OS® XL C/C++ treats the beginning of the first comment as the end of the in-stream data set. To avoid this occurrence, you can change the delimiter by specifying DLM=nn, where nn is a two-character delimiter, on the DD statement that identifies the file. For example: 
   //MYDD   DD *,DLM=@@
   #include <stdio.h>
   /* Hello, world program */
   int main() {printf("Hello, world\n"); }
   @@

For more information about in-stream data sets, see z/OS MVS JCL User's Guide.

To open an in-stream data set, call the fopen() or freopen() library function and specify the ddname of the data set. You can open an in-stream data set only for reading. Specifying any of the update, write, or append modes fails. Once you have opened an in-stream data set, you cannot acquire or change the file position except by rewinding. This means that calls to the fseek(), ftell(), fgetpos(), and fsetpos() for in-stream data sets fail. Calling rewind() causes z/OS XL C/C++ to reopen the file, leaving the file position at the beginning.

You can concatenate regular sequential data sets and in-stream data sets. If you do so, note the following:
  • If the first data set is in-stream, you cannot acquire or change the file position for the entire concatenation.
  • If the first data set is not in-stream and supports repositioning, you must specify the noseek parameter on the fopen() or freopen() call that opens the concatenation. If you do not, fopen() or freopen() opens the file successfully; however, an error occurs when the read position gets to the in-stream.
  • The in-stream data set is treated as FB 80 and the concatenation rules for sequential concatenation apply.